Punching and nibbling machines work sheet metal by co-action between an axially reciprocating punch and a fixed die. During a portion of its stroke the punch has its lower free end surface between the upper side and underside of the plate. Continuous punching or nibbling signifies that the punch step by step removes a small portion of plate during each stroke. During this operation the plate is kept still, subsequently to be fed forward a small distance for the next stroke. The plate is thus fed discontinuously.
For duplicating a given pattern by means of punching or nibbling, coordinate guiding devices are used together with the punching and nibbling machine. These devices usually comprise two slides arranged for travel at right angles to each other. If the machine has a generally planar, U-shaped frame with a gap, the coordinate guiding means can be disposed in the gap of the machine, one slide being adapted on fixed runners for movement in the lengthwise extension of the gap and the other slide being adapted on guides or runners on the first slide for movement at right angles to the lengthwise direction of the gap. The workpiece in the shape of a plate is clamped to the latter slide and can thus be moved relative to the fixed working position of the punch and die, whereby a desired pattern can be cut in the plate.
To achieve duplication of such a pattern, a template can be used, which guides a pin or template follower connected to the second slide. The pin can be taken manually along the profile of the template or can, for example, be steered into holes in the template for punching individual holes in the plate. One usually works with a system consisting of two coordinates mutually at right angles.
The duplication can be automated with the aid of driving motors connected to respective slides. These driving motors then move the workpiece in the desired coordinate directions according to a definite program. Such an arrangement allows entirely automated copying of a certain pattern, the program being introduced into a computer and stored in its memory in some suitable way, e.g. directly from a drawing. The computer controls the driving motors. These known apparatuses work satisfactorily, but have the disadvantage that the motors must develop large power for the rapid movement of the slides and workpiece between each punching operation, when large inertia forces must be overcome. The whole apparatus will further more be relatively complicated and expensive and must be operated by skilled personnel, both at the machine and in the prepatory work for taking the program from the drawing.